The present invention relates to improvements in portable impact tools in general, and more particularly to improvements in portable apparatus which can be used with particular advantage for driving nails, U-shaped staples or analogous fasteners into pieces of wood, concrete; plastic or the like.
It is already known to employ an electromagnet as a means for applying forces to a reciprocable impeller which serves to drive successive nails, staples or like fasteners into pieces of wood or the like. It is also known to impart to the impeller the shape of a blade and to secure such impeller directly to the reciprocable armature of an electromagnet. When the impeller is retracted, the apparatus allows or causes a fresh fastener to advance in front of the retracted impeller, and the latter thereupon receives an impulse to perform a forward stroke which results in expulsion of the freshly admitted fastener from the apparatus and into the material of a workpiece.
It is further known to regulate the magnitude of impacts which the impeller transmits to a fastener by energizing the electromagnet with several full waves or half waves of electric current. It is equally known to regulate the forces which are transmitted by an electric impact stapler or the like in accordance with the so-called phase operating angle principle.
A drawback of presently known apparatus of the above outlined character is that a mere regulation of the magnitude or intensity of an impact does not always suffice to ensure optimum introduction of a fastener into a workpiece. Moreover, conventional proposals are unsatisfactory on the additional ground that the energy consumption is very high and that the apparatus must be designed to receive or generate large currents in order to be in a position to regulate the magnitude of impacts within a desired range. The application of large currents necessitates appropriate measures to avoid overloading of the network. Still further, when the fasteners must be driven home in response to the application of large forces, the parts of the apparatus are subjected to very pronounced stresses so that the useful life of such apparatus is short and/or the apparatus require frequent inspection, maintenance and repair.
In many instances, the introduction of a nail, staple or the like into a workpiece in response to the application of a single impulse to an impeller which is used to drive the fastener home is highly undesirable and unsatisfactory because the abruptly introduced fastener is likely to damage the surface of the workpiece around the locus of introduction or in response to bending as a result of the application of a very pronounced impact. Furthermore, a tool which can generate and abruptly apply very large forces is dangerous since it can be used as a gun which is capable of propelling a projectile through a considerable distance and in such a way that the projectile can cause serious injuries or death at a locus which is remote from the apparatus.